Using a Virtual Internet Protocol Address to Represent Dually Connected Hosts in an Internet Protocol Overlay Network

ABSTRACT

Techniques are presented herein for distributing address information of host devices in a network. At a first router device, a packet is received from a first host device that is destined for a second host device. The first host device is dually-connected to the first router and a second router device. The second router device is part of a virtual port channel pair with the first router device. A message is sent to the second router device, the message indicating that the first host device is connected to the second router device. The packet is encapsulated with an overlay header and is sent to a third router device that is connected to the second host device. The encapsulated packet contains a Layer 2 address associated with the first host device and a Layer 3 address associated with the first host device.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 14/873,572, filed Oct. 2, 2015, which is in turn a continuationof U.S. patent application Ser. No. 13/853,128, filed Mar. 29, 2013. Theentirety of each of these applications is incorporated herein byreference.

TECHNICAL FIELD

The present disclosure relates to enabling communications between hostdevices in a network environment.

BACKGROUND

In typical network environments, host devices (“hosts”) can connect to anetwork via one or more network devices that are routers and/or switches(“routers”). Multiple communication links may be present between thehosts and the routers. The communication links may be “active-active”communication links that enable communications between the hosts and aplurality of the routers via, e.g., a virtual port channel (vPC). In the“active-active” communication mode, each of the routers is configured tomanage traffic to and from a host device, and in the event of a failureof one router, the other routers manage the traffic until the issueassociated with the failed router is resolved. The communication linksmay also be “active-passive” communication links, where only one of therouters is configured to manage traffic to and from a host device, andin the event of a failure of the active router, the other inactiverouters are “activated” in order to handle the communications associatedwith the host device.

These communication links may be part of a Layer 2 Ethernet channel. Thehosts may be configured to host virtual machines. The virtual machinesmay send communications (e.g., packets) to each other. Virtual machinesmay “move” within the network when they are reassigned or otherwisehosted by different physical servers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example network topology including a plurality ofrouters that are configured to distribute address information associatedwith host devices in an Internet Protocol based overlay network.

FIGS. 2A and 2B show examples of address information and routing pathinformation stored in routing tables of the routers in the network.

FIG. 3 shows an example of a router in the network with multiplephysical ports that are configured to interface with one or more hostdevices in the network.

FIG. 4 shows an example flow chart depicting operations performed by oneor more of the plurality of routers to distribute the addressinformation of the host devices in the network.

FIG. 5 shows an example block diagram of a router device that isconfigured to distribute the address information of the host devices inthe network.

DESCRIPTION OF EXAMPLE EMBODIMENTS Overview

Techniques are presented herein for associating virtual addressinformation with a dually-connected host device and distributing thevirtual address information in a network. At a first router device in anetwork, a packet is received from a first host device that is destinedfor a second host device in the network. The first host device isdetermined to be dually-connected to the first router device and asecond router device in the network. The second router device is part ofa virtual port channel pair with the first router device. When it isdetermined that the first host device is dually-connected to the firstrouter device and the second router device, a message is sent to thesecond router device indicating that the first host device is connectedto the second router device. The packet received from the first hostdevice is encapsulated with an overlay header. The encapsulated packetis sent to a third router device that is connected to the second hostdevice. The encapsulated packet contains a Layer 2 address associatedwith the first host device and a Layer 3 address associated with thefirst host device.

EXAMPLE EMBODIMENTS

The techniques described hereinafter involve distributing addressinformation associated with host devices in a network to a plurality ofrouters in the network. An example topology (hereinafter “network”) isshown at reference numeral 100 in FIG. 1. The network 100 (e.g., anoverlay network) comprises a plurality of router devices (“routers”),e.g., three routers in the example of FIG. 1, shown at referencenumerals 102(1)-102(3). It should be appreciated that the term “router”as used herein may refer to a network device that is a router and/orswitch. Router 102(1) may be referred to hereinafter as “router 1” or“R1,” router 102(2) may be referred to hereinafter as “router 2” or “R2”and router 102(3) may be referred to hereinafter as “router 3” or “R3.”FIG. 1 also shows a plurality of host devices (“hosts”), e.g., threehost devices in the example of FIG. 1, shown at reference numerals104(1)-104(3). Host device 104(1) may be referred to hereinafter as“host 1” or “H1,” host device 104(2) may be referred to hereinafter as“host 2” or “H2,” and host device 104(3) may be referred to hereinafteras “host 3” or “H3.”

Each of the hosts 104(1)-104(3) may be dually-connected to two of therouters 102(1)-102(3). For example, as shown in FIG. 1, host 1 isdually-connected to router 1 and router 2 using port channel technology.That is, router 1 and router 2 belong to a virtual port channel (vPC)pair. Router 1 and router 2 are vPC peers connected via a peer link.Router 1 and router 2 are both configured to manage communications toand from host 1. As members of the vPC pair, router 1 and router 2 maypresent a single logical port (shown as port “P” in FIG. 1) to host 1,and this logical port may be mapped to physical ports on each of router1 and router 2. Thus, host 1 is said to be “dually-connected” or“dually-homed” to both router 1 and router 2. From the perspective ofhost 1, it is logically connected to a single port, which is the vPClogical port that is presented to host 1 by router 1 and router 2. Fromthe perspective of router 1 and router 2, a physical port of each ofrouter 1 and router 2 is dedicated to service communications to and fromhost 1, and these physical ports are mapped to the logical vPC portpresented to host 1.

Also, as shown in FIG. 1, host 2 may be connected to a physical port ofrouter 3, and host 3 may be connected to a physical port of router 1.Thus, router 3 is configured to manage communications to and from host2, and router 1 is configured to manage communications to and from host3. Host 2 and host 3 are not dually-homed since they are not connectedto a router via a vPC port.

Host 1, host 2 and host 3 are depicted in FIG. 1 as belonging to thesame broadcast group or “bridge domain,” which is depicted at referencenumeral 106. For example, the bridge domain 106 may be a virtual localarea network (VLAN) that includes host 1, host 2 and host 3. The bridgedomain 106 is identified by a particular identifier (e.g., a virtualnetwork identifier or VNI), and packets that are sent to devices (e.g.,host 1 to host 3) in the bridge domain 106 are configured with thisparticular identifier. In one example, the bridge domain 106 isidentified with a VNI identifier of “20,” as shown in FIG. 1.

FIG. 1 also shows an overlay Internet Protocol (IP) fabric 108. Theoverlay IP fabric 108 is a network that includes routers 102(1)-102(3)and allows the routers 102(1)-102(3) to send encapsulated IP packets toeach other, as described according the techniques presented herein. Forexample, host 1 may exchange communications with host 2 by exchangingencapsulated IP packets across the overlay IP fabric 108 via therespective routers associated with host 1 and host 2, as describedherein.

Each of the host devices 104(1)-104(3) is assigned an Open SystemsInterconnection (OSI) Layer 2 Media Access Control (MAC) address. Forexample, the MAC address of each of the host devices 104(1)-104(3) maybe assigned by a manufacturer of the host devices. The MAC address forhost 1 may be referred to hereinafter as “M1,” the MAC address for host2 may be referred to hereinafter as “M2” and the MAC address of host 3may be referred to hereinafter as “M3.” The routers 102(1)-102(3) areassigned IP addresses (e.g., Layer 3 addresses). Additionally, as statedabove, since router 1 and router 2 belong to a vPC router pair, the vPCrouter pair itself is assigned a virtual IP (vIP) address. For example,FIG. 1 shows the IP address of router 1 as “1.1.1.1/32,” the IP addressof router 2 as “2.2.2.2/32,” the IP address of the vPC router pair(comprised of router 1 and router 2) as “3.3.3.3/32” and the IP addressof router 3 as “4.4.4.4/32.” It should be appreciated that these IPaddresses are merely examples, and that the IP addresses may be any IPaddress in compliance with IP version 4 (IPv4) and IP version 6 (IPv6)protocols.

As stated above, the host devices 104(1)-104(3) may exchangecommunications with each other across the overlay IP fabric 108. Forexample, host 1, which is managed by both router 1 and router 2 (thatbelong to a vPC router pair), may exchange communications with host 2,which is managed by router 3. Host 1 is connected to a logical vPC portthat enables host 1 to communicate with both router 1 and router 2 toexchange communications in the network 100. In one example, host 1 mayutilize its link (e.g., an Ethernet channel) to router 1 to send apacket that is destined for host 2. For example, the packet may be anAddress Resolution Protocol (ARP) broadcast request message to requestan address (e.g., a MAC address or an IP address) of host 2. The ARPbroadcast request message lists the source address as the MAC address ofhost 1 (“M1”). Router 1, upon receiving the packet, obtains the sourceaddress listed in the packet, and identifies this source address as theMAC address corresponding to host 1. Since router 1 is alreadyconfigured to manage host 1, the router 1 will already have the MACaddress of router 1 stored in its routing table. Thus, upon receivingthe packet, router 1 will look-up the source address in its routingtable and will determine that the MAC address for host 1 is a localaddress since it is already stored in the routing table of router 1.Router 1 is also able to identify that host 1 is dually-homed to bothrouter 1 and router 2 by evaluating the port on which the packet wasreceived. As described above, since router 1 and router 2 are part of avPC router pair, router 1 and router 2 present a single logical port(that is mapped to a physical port on both router 1 and router 2) tohost 1. Thus, if the packet is received by router 1 at the physical portthat is mapped to the single logical port, router 1 is able to determinethat the packet was received from a device that is dually-homed with theother router device in its vPC router pair (i.e., router 2).

Upon determining that host 1 is dually-homed, router 1 sends a messageto router 2 to indicate to router 2 that host 1 is linked to both router1 and router 2 via the vPC port. Router 2 receives this message andstores the MAC address of host 1 in its routing table forsynchronization between router 2 and router 1. In one example, router 2may already have prior knowledge of the MAC address of host 1 since itis part of a vPC pair with router 1. In this example, router 2 receivesthe message and stores an IP address, e.g., a virtual IP (“vIP”) addressthat is commonly associated with router 1 and router 2 in the vPC pair.After sending the message to router 2, router 1 then encapsulates theoriginal packet with an overlay IP header. The overlay IP header liststhe destination address as an address associated with a destinationrouter (e.g., router 3) and lists the source address as the vIP addressassociated with the vPC router pair of router 1 and router 2 (i.e., IPaddress “3.3.3.3/32” as shown in FIG. 1 and described above).

When the router 1 sends the encapsulated packet with the overlay IPheader to the overlay IP fabric 108, router 3 receives the encapsulatedpacket. Upon receiving the packet, router 3 undergoes an “addresslearning” process. That is, since router 3 has not received any priorpacket originating from host 1, router 3 undergoes the address learningprocess in order to obtain the MAC address associated with host 1 and tostore it in its routing table.

Router 3 also evaluates the source IP address of the IP overlay header,and determines that host 1 is reachable through the IP address thatcorresponds to the source IP address in the IP overlay header (i.e., thevIP for the vPC pair of router 1 and router 2). Router 3 stores thisaddress information in its routing table. Thus, router 3, upon receivingthe encapsulated packet from router 1 stores two types of addressinformation in its routing table: the Layer 2 MAC address associatedwith host 1 and the Layer 3 IP address that corresponds to the source IPaddress in the IP overlay header. If, as in this example, the IP addressin the overlay header corresponds to a vIP of a vPC router pair, thenrouter 3 stores the vIP address as the IP address associated withhost 1. If the IP address corresponds to a standard IP address of arouter, then router 3 stores that IP address as the IP address. Forexample, in FIG. 1, host 3 is connected only to router 1 and is notdually-homed. Thus, router 1 uses its own standard IP address foroverlay encapsulation for packets originating from host 3, andaccordingly, when the address learning techniques for host 3 areperformed, the router 3 will store the standard IP address associatedwith router 1 (e.g., IP address “1.1.1.1/32” in FIG. 1) and willassociate the standard IP address of router 1 with host 3. Router 3 andother such routers in the network will have no special knowledge of thevIP address used by the routers in the vPC pair (e.g., the vIP addressused by router 1 and router 2).

After receiving the encapsulated packet from router 1, router 3de-encapsulates the packet by removing the IP overlay header and sendsthe ARP request message to host 2. Host 2, upon receiving the ARPrequest message, sends a unicast ARP response message, with thedestination address set to the MAC address associated with host 1 andthe source address associated with the MAC address of host 2. Router 3receives the unicast ARP response message from host 2, and encapsulatesthe packet with an IP overlay header. In this encapsulated packet, thesource address corresponds to the IP address of router 3 and thedestination address is associated with the vIP address associated withthe vPC router pair (due to router 3 learning the vIP address uponreceiving the initial encapsulated packet from router 1). Since thereare two potential paths to reach a router in the vPC pair (e.g., a pathfrom router 3 to router 1 and a path from router 3 to router 2), router3 selects a best path (e.g., an OSI layer 3 Equal Cost Multipath (ECMP)path) to reach the devices associated with the vIP (i.e., router 1 orrouter 2). For example, router 3 may select an ECMP best path to reachrouter 2. Router 2 receives the encapsulated packet and de-encapsulatesit by removing the IP overlay header. Router 2 then evaluates the ARPresponse packet (resulting from the de-encapsulation), and identifiesthe destination address as that corresponding to the MAC address forhost 1. Since router 2 had previously received the MAC addressinformation of host 1 during the packet exchange between router 1 androuter 2 (when router 1 received the initial ARP request packet fromhost 1), router 2 sends the ARP response packet to host 1 via thephysical port of router 2 that is mapped to the vPC port that islogically connected to host 1. Additionally, by receiving theencapsulated packet from router 3, router 2 is able to undergo theaddress learning process to learn the MAC address associated with host 2and is able to determine that host 2 is reachable through the IP addressassociated with router 3. Since router 1 and router 2 are vPC routerpairs, router 2 sends a message with this information to router 1, thusinforming router 1 of the MAC address associated with host 2 and thathost 2 is reachable via the IP address associated with router 3. Router1 and router 2 store this information in their respective routingtables. Subsequently, any unicast packet exchange between host 1 andhost 2 will use the vIP and IP address of router 3 as the source IP anddestination IP, respectively, in the overlay IP header as the packetsare encapsulated.

Reference is now made to FIGS. 2A and 2B. FIGS. 2A and 2B show examplesof address information and routing path information stored in routingtables of a router (e.g., router 3) in the network 100. FIG. 2A showsthe address information (e.g., the Virtual Tunnel Endpoint (VTEP)address or IP address) 202 stored in router 3. For example, routers thatperform overlay encapsulation and de-encapsulation are also called VTEPdevices. This distinguishes them from regular routers (i.e., “transitrouters”) that are unaware of overlay encapsulation. The addressinformation 202 comprises the MAC address associated with each host inthe network 100, as well as the IP address or vIP address, as the casemay be, of the router or vPC router pair that manages each host. Forexample, address information 202 comprises the MAC address “M1”associated with host 1, the MAC address “M2” associated with host 2 andthe MAC address “M3” associated with host 3. These MAC addresses arestored in the routing table by the routers using the address learningtechniques described above. The MAC address for each host is mapped tothe corresponding IP addresses or vIP address associated with therouters that manage the host devices. For example, MAC address “M1” ismapped to vIP address “3.3.3.3/32” associated with the vPC router pairincluding router 1 and router 2. MAC address “M2” is mapped to the IPaddress “4.4.4.4/32” associated with router 3. MAC address “M3” ismapped to the IP address “1.1.1.1/32” associated with router 1. Theaddress information also contains the VNI that identifies the bridgedomain 106 to which the hosts belong.

The routing path information is shown at reference numeral 204 in FIG.2B. In FIG. 2B, each of the IP addresses (and vIP address) are mapped toa corresponding router via a router path. FIG. 2B shows, in general,typical routing information for a given set of IP destinations in an IProuter. For example, IP address “1.1.1.1/32” is associated with router1, and thus, the routing path associated with IP address “1.1.1.1/32”routes communications for router 1. The routing path information 202shows a similar routing path for IP address 2.2.2.2/32, which is mappedto router 2. The routing path for vIP address “3.3.3.3/32” routes toboth router 1 and router 2, since router 1 and router 2 belong to a vPCrouter pair that is associated with the vIP address. The routing pathinformation 204 also shows the routing path costs associated with eachof the routing paths. FIG. 2B also shows a routing path cost that isassociated with each IP address. The routing path cost is in indicatorof how close or far a specific route is from a reachability perspectiveof one or more of the routers. Routers often choose the shortest or bestpath to reach a specific destination (e.g., path with the lowestrelative cost). The routing path cost values shown in FIG. 2B may berelative to one another, where relatively low routing path costsindicate relatively high levels of reachability and where relativelyhigh routing path costs indicate relatively low levels of reachability.

Reference is now made to FIG. 3, which shows an example of a router(e.g., router 1) in the network 100 with multiple physical ports. InFIG. 3, router 1 has two physical ports, shown at P1 and P2. Port P1 isconnected to host 3, while port P2 is part of a vPC pair that isconnected to host 1. The router 102(1) maintains a table that identifieswhether or not each of its physical ports is a dually-connected (e.g.,part of a vPC pair) port. As shown in Table 1 below, since port P1 ofrouter 102(1) is not part of a vPC pair, port P1 is notdually-connected. Thus, as shown in Table 2 below, communications thatare received via port P1 (i.e., from host 3) are assigned the IP addressassociated with router 102(1) (e.g., “1.1.1.1/32”). Likewise, as shownin Table 1, since port P2 of router 102(1) is part of a vPC pair, portP2 is a dually-connected port and is logically connected to the vPC port“P” in FIG. 1 that is presented to host 1. Therefore, as shown in Table2, communications that are received via port P2 (i.e., from host 1 areassigned the vIP address associated with the vPC router pair (e.g.,“3.3.3.3/32”). In Table 2, the Remote and Bridging fields indicate thata frame has been encapsulated on a remote endpoint (e.g., not on aswitch or its vPC peer). In such cases, traffic may be forwarded basedon an outer IP destination or a packet, though a source IP address mayremain unchanged.

TABLE 1 Port connectivity Port/Logical Interface Dually-connected? P1 NP2 Y

TABLE 2 Egress communications table Originator Source-IP to useLocal/Singly-connected R1 - IP = “1.1.1.1/32” Local/Dually-connected vIP= “3.3.3.3/32” Remote and Bridging Keep the source IP

Reference is now made to FIG. 4. FIG. 4 shows an example flow chart 400depicting operations performed by one or more of the plurality ofrouters to distribute the address information of the host devices in thenetwork. At 405, a packet is received from a first host device that isdestined for a second host device in the network. At 410, adetermination is made that the first host device is dually-connected tothe first router device and a second router device in the network. Thesecond router device, for example, is part of a vPC pair with the firstrouter device. At operation 415, a message is sent to the second routerdevice, the message indicating that the first host device is connectedto the second router device. In one example, the first host device maybe connected to the second router device via a vPC link (or anothersynchronization link) between the first host device and the secondrouter device At operation 420, the packet received from the first hostdevice is encapsulated with an overlay header. At operation 425, theencapsulated packet is sent to a third router device that is connectedto the second host device. The encapsulated packet may be sent to thethird router device via a best available path in the network.

Reference is now made to FIG. 5, which shows an example of a blockdiagram of a router device (“router”) configured to distribute theaddress information of the host devices in the network. The routerdevice is shown generally at reference numeral 102, though it should beappreciated that the router device 102 may represent any of the routers102(1)-102(3) described in connection with FIG. 1 above.

The router 102 comprises, among other components, a plurality of ports502, a router application specific integrated circuit (ASIC) 504, aprocessor 506 and a memory 508. The ports 502 receive communications(e.g., packets) from host devices in a network and send communicationsto devices in the network 100. The ports 502 are coupled to the routerASIC 504. The router ASIC 504 forwards the packets to an appropriate oneof the ports 502 for transmission to a destination network device in thenetwork. The router ASIC 504 is coupled to the processor 506. Theprocessor 506 is, for example, a microprocessor or microcontroller thatis configured to execute program logic instructions (i.e., software)stored in memory 508 for carrying out various operations and tasks ofthe router 102, as described above. For example, the processor 506 isconfigured to execute address assignment and routing table updateprocess logic 510 to assign an address to packets originating from hostdevices and to update its routing table database, shown at referencenumeral 512, with address information of the host devices.

The functions of the processor 506 may be implemented by logic encodedin one or more tangible computer readable storage media or devices(e.g., storage devices compact discs, digital video discs, flash memorydrives, etc. and embedded logic such as an ASIC, digital signalprocessor instructions, software that is executed by a processor, etc.).

The memory 508 may comprise read only memory (ROM), random access memory(RAM), magnetic disk storage media devices, optical storage mediadevices, flash memory devices, electrical, optical, or otherphysical/tangible (non-transitory) memory storage devices. The memory508 stores software instructions for the address assignment and routingtable update process logic 510. Thus, in general, the memory 508 maycomprise one or more computer readable storage media (e.g., a memorystorage device) encoded with software comprising computer executableinstructions and when the software is executed (e.g., by the processor506) it is operable to perform the operations described for the addressassignment and routing table update process logic 510.

The address assignment and routing table update process logic 510 maytake any of a variety of forms, so as to be encoded in one or moretangible computer readable memory media or storage device for execution,such as fixed logic or programmable logic (e.g., software/computerinstructions executed by a processor), and the processor 506 may be anASIC that comprises fixed digital logic, or a combination thereof.

For example, the processor 506 may be embodied by digital logic gates ina fixed or programmable digital logic integrated circuit, which digitallogic gates are configured to perform the address assignment and routingtable update process logic 510. In general, the process logic 510 may beembodied in one or more computer readable storage media encoded withsoftware comprising computer executable instructions and when thesoftware is executed operable to perform the operations describedhereinafter.

It should be appreciated that the techniques described above inconnection with all embodiments may be performed by one or more computerreadable storage media that is encoded with software comprising computerexecutable instructions to perform the methods and steps describedherein. For example, the operations performed by the routers may beperformed by one or more computer or machine readable storage media(non-transitory) or device executed by a processor and comprisingsoftware, hardware or a combination of software and hardware to performthe techniques described herein.

In sum, a method is provided comprising: at a first router device in anetwork, receiving a packet from a first host device that is destinedfor a second host device in the network; determining that the first hostdevice is dually-connected to the first router device and a secondrouter device in the network, wherein the second router device is partof a virtual port channel pair with the first router device; when it isdetermined that the first host device is dually-connected to the firstrouter device and the second router device, sending to the second routerdevice a message indicating that the first host device is connected tothe second router device; encapsulating the packet received from thefirst host device with an overlay header; and sending the encapsulatedpacket to a third router device that is connected to the second hostdevice, wherein the encapsulated packet contains a Layer 2 addressassociated with the first host device and a Layer 3 address associatedwith the first host device.

Additionally, an apparatus is provided, comprising: a plurality ofports; a memory; and a processor coupled to the memory and configuredto: receive a packet from a first host device that is destined for asecond host device in the network; determine that the first host deviceis dually-connected to a first router device and a second router devicein the network, wherein the second router device is part of a virtualport channel pair with the first router device; when it is determinedthat the first host device is dually-connected to the first routerdevice and the second router device, generate a message to be sent tothe second router device, the message indicating that the first hostdevice is connected to the second router device; encapsulate the packetreceived from the first host device with an overlay header; and causethe encapsulated packet to be sent to a third router device that isconnected to the second host device, wherein the encapsulated packetcontains a Layer 2 address associated with the first host device and aLayer 3 address associated with the first host device.

In addition, a computer-readable storage media is provided that isencoded with software comprising computer executable instructions andwhen the software is executed it is operable to: receive a packet from afirst host device that is destined for a second host device in thenetwork; determine that the first host device is dually-connected to afirst router device and a second router device in the network, whereinthe second router device is part of a virtual port channel pair with thefirst router device; when it is determined that the first host device isdually-connected to the first router device and the second routerdevice, send to the second router device a message indicating that thefirst host device is connected to the second router device; encapsulatethe packet received from the first host device with an overlay header;and cause the encapsulated packet to be sent to a third router devicethat is connected to the second host device, wherein the encapsulatedpacket contains a Layer 2 address associated with the first host deviceand a Layer 3 address associated with the first host device.

The above description is intended by way of example only. Variousmodifications and structural changes may be made therein withoutdeparting from the scope of the concepts described herein and within thescope and range of equivalents of the claims.

What is claimed is:
 1. A method comprising: at a first router device:receiving, on a first physical port mapped to a virtual port having aLayer 3 address, a packet from a first host device having a Layer 2address, wherein the packet is destined for a second host device in thenetwork; encapsulating the packet with an overlay header to generate anencapsulated packet that includes the Layer 3 address of the virtualport and the Layer 2 address of the first host device; and sending theencapsulated packet to a second router device that is connected to thesecond host device to enable the second router device to determine,based on the Layer 2 address, that the first host device is reachablethrough the Layer 3 address.
 2. The method of claim 1, wherein thevirtual port is mapped to a plurality of physical ports including thefirst physical port and a second physical port such that the pluralityof physical ports share the Layer 3 address.
 3. The method of claim 1,wherein the encapsulated packet includes the Layer 3 address as a sourceaddress of the encapsulated packet.
 4. The method of claim 1, furthercomprising: sending, to a third router device having a second physicalport mapper to the virtual port, a message indicating that the firsthost device is connected to the third router device and that the thirdrouter device can ignore learning the Layer 3 address when the thirdrouter device receives the encapsulated packet.
 5. The method of claim4, wherein the message further indicates to the third router device thatthe first host device is accessible by the third router device via alocal link between the third router device and the first host device. 6.The method of claim 1, further comprising: receiving a response packetfrom the second host device; and storing Layer 2 address information andLayer 3 address information associated with the second host device. 7.The method of claim 1, wherein: sending the encapsulated packet includessending the encapsulated packet via a best available path in thenetwork.
 8. An apparatus comprising: a plurality of ports configured tosend and receive communications over a network; a memory; and aprocessor coupled to the memory and configured to: receive, on a firstphysical port mapped to a virtual port having a Layer 3 address, apacket from a first host device having a Layer 2 address, wherein thepacket is destined for a second host device in the network; encapsulatethe packet with an overlay header to generate an encapsulated packetthat includes the Layer 3 address of the virtual port and the Layer 2address of the first host device; and send the encapsulated packet to asecond router device that is connected to the second host device toenable the second router device to determine, based on the Layer 2address, that the first host device is reachable through the Layer 3address.
 9. The apparatus of claim 8, wherein the virtual port is mappedto a plurality of physical ports including the first physical port and asecond physical port such that the plurality of physical ports share theLayer 3 address.
 10. The apparatus of claim 8, wherein the encapsulatedpacket includes the Layer 3 address as a source address of theencapsulated packet.
 11. The apparatus of claim 8, wherein the processoris further configured to: send, to a third router device having a secondphysical port mapper to the virtual port, a message indicating that thefirst host device is connected to the third router device and that thethird router device can ignore learning the Layer 3 address when thethird router device receives the encapsulated packet.
 12. The apparatusof claim 11, wherein the message further indicates to the third routerdevice that the first host device is accessible by the third routerdevice via a local link between the third router device and the firsthost device.
 13. The apparatus of claim 8, wherein the processor isfurther configured to: receive a response packet from the second hostdevice; and store Layer 2 address information and Layer 3 addressinformation associated with the second host device.
 14. The apparatus ofclaim 8, wherein the processor is configured to send the encapsulatedpacket by sending the encapsulated packet via a best available path inthe network.
 15. A non-transitory computer-readable storage mediaencoded with software comprising computer executable instructions andwhen the software is executed operable to: receive, on a first physicalport mapped to a virtual port having a Layer 3 address, a packet from afirst host device having a Layer 2 address, wherein the packet isdestined for a second host device in the network; encapsulate the packetwith an overlay header to generate an encapsulated packet that includesthe Layer 3 address of the virtual port and the Layer 2 address of thefirst host device; and send the encapsulated packet to a second routerdevice that is connected to the second host device to enable the secondrouter device to determine, based on the Layer 2 address, that the firsthost device is reachable through the Layer 3 address.
 16. Thecomputer-readable storage media of claim 15, wherein the virtual port ismapped to a plurality of physical ports including the first physicalport and a second physical port such that the plurality of physicalports share the Layer 3 address.
 17. The computer-readable storage mediaof claim 15, wherein the encapsulated packet includes the Layer 3address as a source address of the encapsulated packet.
 18. Thecomputer-readable storage media of claim 15, further comprisinginstructions operable to send, to a third router device having a secondphysical port mapper to the virtual port, a message indicating that thefirst host device is connected to the third router device and that thethird router device can ignore learning the Layer 3 address when thethird router device receives the encapsulated packet.
 19. Thecomputer-readable storage media of claim 18, wherein the message furtherindicates to the third router device that the first host device isaccessible by the third router device via a local link between the thirdrouter device and the first host device.
 20. The computer-readablestorage media of claim 15, further comprising instructions operable to:receive a response packet from the second host device; and store Layer 2address information and Layer 3 address information associated with thesecond host device.